1. Field of the Invention
The present invention relates to a storage control device and a data recovery method for the storage control device.
2. Description of the Related Art
The storage control device generates RAID (Redundant Array of Independent Disks)-based redundant storage areas by using a plurality of disk drives such as hard disk drives, for example, and provides a host computer (‘host’ hereinbelow) with the storage areas. Even when a fault occurs in any of the disk drives in the storage areas made redundant through RAID, the storage capacity of the disk drive in which the fault occurred can be restored on the basis of the storage capacity stored in another disk drive.
In the prior art, when the number of errors occurring in a certain disk reaches a specified value of a first level, mirroring is started between the disk and spare disk. When the number of errors occurring in the disk reaches a specified value of a second level, mirroring is canceled and the operation is continued by using the spare disk (Japanese Patent Application No. 2005-100259).
In the prior art that appears in Japanese Patent Application No. 2005-100259, the reliability of the storage control device is raised by using the spare disk but the relationship between preventative copying to the spare disk and the restoration of data using a parity disk is not adequately considered and provides a margin for improvement.
For example, a case where data are not read due to the occurrence of a fault in the copy source disk before preventative copying to the spare disk is completed may be considered. In this case, data restoration work based on parity data is started. However, because the data restoration work is not synchronized with the preventative copying to the spare disk, data restoration work is performed with respect to all of the stored content of the disk in which the fault occurred irrespective of whether the preventative copying is complete.
Therefore, it takes a long time for the data restoration work to be completed and the response performance of the storage control device also drops. In particular, because of the advances in the increased capacity of disks in recent years, the time required for the data restoration work also readily grows. In addition, although there are differences depending also on the RAID level, when a fault occurs in another disk during the period until completion of the data restoration work, data can no longer be restored. In the case of RAID5, one disk fault can be tolerated and, with RAID6, up to two disk faults can be tolerated at the same time. In a RAID group in which data restoration work is being performed, the reliability drops during the period until the data restoration work is completed.